The Postmenopausal Estrogen/Progestins Intervention (PEPI) trial, conducted and seven clinical centers around the United States, is a randomized double-blind placebo-controlled trial of hormone treatment in 875 postmenopausal women. Women were recruited from the community during a 16 month period, and will be treated for three years. Treatment aims are 1) placebo; 2) unopposed Premarin; 3) Premarin plus cyclic Provera; 4) Premarin plus continuous Provera; and 5) Premarin plus micronized progesterone. The primary endpoints are HDL-cholesterol, postchallenge insulin, fibrinogen and systolic blood pressure -- in the context of their metabolic and physiologic covariates. Additional major outcomes of interest include bone mineral density, quality of well-being, and endometrial pathology. As a cooperative agreement, PEPI employs standardized methods, central laboratories and a single coordinating center.